1. Field of the Invention:
This invention relates to a control system for electronic engine control for computing various controlled variables by a digital processor, and more particularly to a system of reading the input signal from a temperature sensor which detects the engine temperature.
2. Description of the Prior Art:
The input signal from a water temperature sensor for detecting cooling water temperature (which is closely related to the engine temperature) is an important factor in computing fuel injection amount during an engine start period and during engine warming-up after the start period. An analog sensor signal may be for example, A-D (Analog-Digital) converted and read at predetermined intervals of time during operation of the engine. In prior control systems for electronically controlled fuel injection engines, frequency of reading the input signal from the water temperature sensor during the start period is equal to that after the start period (in this specification the start period means a period from start and operation of a starting motor to occurrence of complete explosion, and post-start period means a period during which the engine is operated after the complete explosion, complete explosion being self-sustained engine operation not requiring the starting motor operation) and does not vary. The water temperature sensor generally contains a thermistor to which voltage related to voltage of an accumulator is applied. The voltage of the accumulator in the temperature sensor varies (or fluctuates) greatly in the start period because current is supplied to the starting motor, so that the input signal from the water temperature sensor also fluctuates greatly. Thus, prior systems for reading the input signal from the water temperature sensor during the start period were subject to greatly deviating signals due to this accumulator voltage variation so that fuel injection amount, for example, are computed on the basis of that great deviation for a relatively long time until the next reading, causing loss to accuracy in control. However, after the start period the cooling water temperature has relatively small time-based variation compared with other detected parameters, and any reduction in the frequency of reading the cooling water temperature also reduces the frequency of reading other parameters after the start period, which is not advantageous for accuracy in engine control after the start period.